Data deduplication is used as a technique for reducing disk capacity requirements in storage apparatuses (RAID, or Redundant Arrays of Independent Disks). One known deduplication function is, for example, to compare data written by a server on a block-by-block basis, and assign the same reference destination if the same data patterns are identified and then hold the data in a disk.
Another known technique is a remote copy function for duplicating data between storage apparatuses to thereby implement mirroring or backup services. In the case of creating a remote copy between the storage apparatuses, deduplicated data is transferred with desired part of a virtual volume defined as the target of the remote copy. Thus, by transferring such deduplicated data stored in a storage pool, the remote copy operation is able to reduce the amount of data transfer.
See, for example, Japanese Laid-open Patent Publication Nos. 2009-251725 and 2008-65425.
However, in the case where a storage device defines deduplicated data in a storage pool as a transfer target, all already allocated blocks in the storage pool are subject to a copy operation. For this reason, such a remote copy operation includes virtual volumes not needed to be backed up as its transfer targets. Therefore, the remote copy operation involves an undesirable increase in the amount of data transfer when there is a lot of data not needed to be backed up. In addition, this remote copy operation causes a copy-destination storage apparatus to consume the same storage space in its storage pool as to a copy-source storage apparatus.
On the other hand, if a part of or the whole virtual volume is allowed to be defined as the transfer target in a remote copy operation, control will be achieved in both the amount of data transfer and the storage space needed to be secured in the storage pool of the copy-destination storage apparatus. However, the remote copy operation defining the virtual volume as the transfer target deals with undeduplicated data deployed in the virtual volume as its transfer target. Therefore, such a remote copy operation tends to have a large amount of data transfer compared to the case of handling deduplicated data as the transfer target.